1. Technical Field
The present invention relates to a disk inspection apparatus and, more particularly, to discrimination of disk deterioration.
2. Related Art
In general, in a CD or DVD rental business or in a disk production process, it is a common practice to polish and restore a disk scratched or contaminated during use of the disk. For example, in a rental shop, a disk which is deeply scratched when used by a user or about which a user claims that reproduction from the disk cannot be performed because of a scratch or the like is reused after polishing the surface of the disk with a special-purpose polisher so that the scratch is erased. Polishing to a depth of about 5 to 10 microns is required to erase a scratch. Therefore, the lower limit of a disk thickness specification of, for example, a DVD disk is reached by polishing about 1 to 5 times.
Meanwhile, a pickup mounted in a CD drive or a DVD drive has an objective lens designed and corrected so as to focus with accuracy in focusing through a disk substrate having a high refractive index when the substrate has a predetermined thickness. If the thickness of the disk substrate is reduced, a spherical aberration occurs and reduces the accuracy of focusing. For this reason, the deterioration in jitter characteristic progresses each time polishing is performed.
JP 10-134527 A discloses a process in which the state of an information recording surface of an optical disk is determined by making a determination as to whether or not an error correction can be made to reproduced data or by computing the number of symbols on which correction has been executed and comparing with a threshold value the result of count of the number of error-correction-failed sequences or the number of sequences on which correction of N symbols or more has been executed, and in which a warning is produced according to the determined state.
JP 3093865 U discloses a process in which while data are being read out from an optical disk and monitored, a track detection position at which the data are discontinuous is recognized as a position at which a scratch exists, while the depth of the scratch is estimated while the pickup is being focused at the scratch on the optical disk; and the optical disk is polished according to the depth of the scratch in a track range in which the scratch exists.
JP 2004-330375 A discloses a process in which the depth and size of a scratch in an optical disk surface are determined and polishing is performed in an optimal fashion according to the determination results.
In a case where a scratch exists in a disk, there is a possibility that the scratch may be removed by polishing the disk surface. However, if the amount of polishing of the disk surface is increased, a spherical aberration is produced and causes a deterioration in jitter characteristic. With respect to a case where a disk having reproduction fault exists, therefore, there is demand for ascertaining, in a short time period, with reliability, whether the cause of deterioration of the disk is a scratch and the disk can be restored if polished, or there is a deterioration in jitter characteristic as a result of excessive polishing and the disk cannot be restored by further polishing. If this cannot be done, there is a possibility of performing useless processing such as processing to further polish a disk which, essentially, has already been polished excessively and for which perform further polishing is meaningless, or processing to discard a disk which is deteriorated essentially due to a scratch and which can be restored if polished.